At the time of start-up of an internal combustion engine having a crankshaft that rotates a plurality of times per one cycle, it is necessary to determine on which stroke each cylinder is in order to set fuel injection timing and ignition timing for that cylinder. Moreover, in order to start the internal combustion engine in a short time, it is necessary to quickly determine the stroke in the cycle of the cylinder.
To meet the above need, Patent Document 1 teaches to set a provisional cylinder discrimination period based on a signal generated by a crank position sensor and, if a cylinder discrimination signal is detected in the provisional cylinder discrimination period, to set the provisional cylinder discrimination period as an actual cylinder discrimination period to determine the stroke in the cycle of the cylinder.
Patent Document 2 teaches to memorize the stopping position of the crankshaft when the operation of an internal combustion engine stops and to estimate the rotational position of the crankshaft at the time of restart of the internal combustion engine based on the memorized stopping position.
Patent Document 3 teaches to disable the sensing by a crank position sensor in a period during which a large voltage fall occurs due to the operation of a starter motor at the time of start-up of the internal combustion engine.
Patent Document 4 teaches to disable the sensing by a crank position sensor during a predetermined period of time since the commencement of the start-up of an internal combustion engine and to detect the top dead center on the compression stroke based on the stopping position of the crankshaft and a rotational change of the crankshaft.